relaydb is a mail header analyzer that builds a database of IP addresses
either known as legitimate senders or spammers.

relaydb doesn't itself classify mails as legitimate or spam; that decision
needs to be reached through other means.  Neither does relaydb block spam
itself.  It merely provides a list of IP addresses to block through other
means, like spamd(8) and pf(4).

relaydb reads a single mail from stdin, analyzes the Received: header
lines and updates blacklist and whitelist counters for each IP address.
